Changes in characteristics of sweet potato flour prepared by different drying techniques

The changes occurring in the characteristics of sweet potato flour as a result of processing were investigated. Pasting behaviour of drum dried and hot air-dried sweet potato flour was determined using Rapid Visco-Analyser. The pasting characteristics decreased due to gelatinization of starch during processing. The degradation of starch by amylases during hot air drying further lowered the water binding capacity/viscosity and total amylose and increased the digestibility compared to those of drum dried and native flour. Swelling power and solubility of the flours increased as a result of processing which subsequently increased with increase in temperature. Scanning electron micrographs of starch granules showed tendency of clustering, especially in drum dried samples. X-ray diffraction patterns showed alteration from Ca-type to V-type with a marked reduction in crystallinity index as a result of processing. The ¹³C NMR spectra of processed starches showed reduced peak intensities and line widths due to depolymerizing effects, and also pointing to their change in crystallinity.     

Physico‐functional and antioxidant properties of purple‐flesh sweet potato flours as affected by extrusion and drum‐drying treatments

Effects of extrusion and drum‐drying treatments on physico‐functional and antioxidant properties of flours prepared from purple‐flesh sweet potato were evaluated. Extrusion variables were feed moisture contents (MC; 10%, 13%, 16%) and screw speeds (SS; 250, 325, 400 r.p.m.), whereas drum‐drying was done at 120, 130 or 140 °C. Effects of MC were generally greater than SS on flour properties. Extruded flours showed higher water absorption and water solubility indices compared with control nonextruded flours. Regardless of SS, total phenolic content and antioxidant activities (DPPH and ABTS) of flours processed at 10% MC were significantly higher than those at 13% and 16%. Both extruded and drum‐dried flours exhibited no peak viscosity, indicating complete gelatinisation of starch. Maximum phenolic content and antioxidant activities of drum‐dried flours were obtained at 140 °C. Although drum‐dried flours had higher antioxidant capacity than extruded flours, both flours could potentially be used as food ingredients.     

Effect of Processing on the Physico-Chemical Characteristics of Quinoa Flour (Chenopodium quinoa,Willd)

The nature and extent of the modification of starch in quinoa, caused by various processes like cooking and autoclaving of the seeds, drum drying of the flour and extrusion of the grits was investigated by measuring the physico-chemical properties - the water absorption, water solubility, swelling power, viscosity and degree of gelatinisation - of the processed samples. Autoclaved samples showed the lowest degree of gelatinisation (32.5% by DSC) of the starch, while the degree of gelatinisation of the precooked/drum dried samples was found to be 97.4% by DSC method. Higher polymer degradation was observed in cooked samples than in autoclaved samples as seen in the gel chromatographic separation. The water solubility in cooked samples (5.44 to 15.58) and in autoclaved samples (7.02 to 9.64) increased with the process time. In the extrusion process, the moisture content as well as the compression ratio was found to affect the degree of starch modification significantly (p <0.01).     

果胶酶酶解预处理对马铃薯泥干燥特性及生粉加工特性的影响

为提高马铃薯生粉的干燥效率,考察了果胶酶酶解预处理不同时间(60~180min)对马铃薯泥热风干燥特性及制备的酶解马铃薯生粉(pectinase-treated native potato flour,PNPF)理化性质和加工特性的影响。结果表明:果胶酶酶解处理降低了马铃薯泥果胶含量和初始含水量,提高了薯泥干燥速率,干燥时间缩短了6.32%~7.81%;果胶酶酶解预处理制备的生粉中果胶、灰分、蛋白质含量显著降低,直链淀粉、支链淀粉和总淀粉含量显著提高,淀粉相对结晶度和生粉碘蓝值降低;同时酶解预处理制备的生粉与未处理生粉相比,具有较高的溶解度和溶胀度,持油性显著降低,持水性提高了40.49%~49.58%,冻融析水率降低了26.23%~62.11%,其中酶解预处理180min制备的生粉(PNPF180)冻融稳定性提升幅度最大;糊化特性分析结果表明,PNPF峰值温度降低,峰值时间缩短,崩解值上升,最终黏度和回生值下降。果胶酶酶解预处理可改善马铃薯泥热风干燥特性,缩短干燥时间,同时显著改善马铃薯生粉基本理化性质及加工特性。     

The pasting behaviour of lactic‐fermented and dried uji (an East African sour porridge)

The effects of sun‐, cabinet‐, and drum‐drying on the behaviour of submerged culture lactic‐fermented pure cassava, maize and finger millet and composites of maize–finger millet and cassava–finger millet were investigated in a Brabender amylograph. The cereal flours and maize–finger millet composite had higher onset and peak gelatinization temperatures but lower peak viscosities than cassava or cassava–finger millet composites. Fermentation alone or in combination with drying increased the viscosity of the flours, except for the fermented and drum‐dried cassava–finger millet composite flour. This increased viscosity of uji on fermentation and drying makes it more difficult to cook. Fermented and drum‐dried flours recorded high initial viscosities, at 30 °C, when the amylograph was switched on. Copyright © 2003 Society of Chemical Industry     

Processing Factors Affecting the Yield and Physicochemical Properties of Starch from Cassava Chips and Flour

Three processing factors, namely, raw materials type (RMT) (i.e. chips and flour) and raw material drying mode (RDM) (i.e. sun‐ and oven‐drying at 55 °C) were related to the yield and some physicochemical properties of starch in a 2³ factorial experiment. The quality characteristics investigated were: moisture content, pH, crude fiber content, peak viscosity and pasting temperature. Starch yields from oven‐dried chips and flour were significantly higher (at 5%) than from sun‐dried materials. The optimal yield of 55.9 g (per 70 g of dried product or 79.9%) was obtained from oven‐dried starch extracted from oven‐dried flour. The peak viscosities (PV) of starches extracted from flour and chips were similar while the observed pasting temperatures of flour‐extracted starches were not significantly different from those derived from chips.     

干燥方法对山药粉性质的影响

通过真空干燥、冷冻真空干燥和喷雾干燥制备山药生/熟粉,研究其流变特性、糊化特性和消化性质,初步探究其变化机制。结果表明,山药生粉具有较高的成糊温度,山药熟粉中冷冻真空干燥山药熟粉的峰值黏度最高(3619.50 cP)。不同干燥方法干燥的山药粉均呈非牛顿流体特性,冷冻真空干燥的山药熟粉的粘弹性最高;山药生粉呈现完整的淀粉颗粒形态,山药熟粉的颗粒形貌差异较大。熟化处理使山药粉抗性淀粉含量显著降低(P<0.05)。熟粉中真空干燥山药熟粉的抗性淀粉含量最高(56.11%)。三种干燥方法中,冷冻真空干燥能较好的保留山药粉的原有理化特性。     

Isoflavone content in soy germ flours prepared from two drying methods

Isoflavone glucosides and aglucons in various soybean varieties (Chiang Mai‐60, S.J.‐5, Chiang Mai‐2, Srisumrong‐1, and Nakhonsawan‐1) harvested from dry vs. rainy seasons were quantified. Isoflavone contents of all soy germs ranged from 16.5 to 30.6 μmol g^?1. Regardless of varieties, isoflavone contents in germ of seeds from dry season were higher (P < 0.05) than those from rainy season. The Chiang Mai‐60 germ, having the highest isoflavone content (30.6 μmol g^?1), was selected for germ flour production. Freeze‐dried germ flour contained higher isoflavone aglucons (17.72 μmol g^?1 daidzein; 6.48 mg g^?1 glycitein; 4.28 μmol g^?1 genistein) than those (15.07; 5.59; 3.41) of drum‐dried germ flour. However, isoflavone glucoside contents in freeze‐dried germ flour (3.27 μmol g^?1 daidzin; 1.86 μmol g^?1 glycitin; 1.41 μmol g^?1 genistin) were lower than those (5.22; 3.15; 1.89) of drum‐dried germ flour. Total isoflavone contents of drum‐dried and freeze‐dried germ flours were comparable (34.32 vs. 35.02 μmol g^?1) but more than that (30.16 μmol g^?1) of unprocessed germ flour.     

Gluten‐free pasta: effect of green plantain flour addition and influence of starch modification on the functional properties and resistant starch content

Green plantain flour (GPF) is rich in indigestible carbohydrates, especially in resistant starch (RS). The objective of this study was to improve the functional pasta properties and RS content by producing gluten‐free (GF) pasta based on rice flour with different amounts of GPF addition (15–60% of total flour blend). Egg albumen (3.5–6.0% of total flour) and dough moisture (36–40%, dough humidity%), at constant emulsifier (0.5% of total flour) addition, were optimised in the first trials. The results showed that an addition up to 30% GPF with higher amount of egg albumen (6%) at dough moisture of 38% provided pasta with acceptable cooking quality and high RS content. Some qualities and/or RS content of GF pasta samples was further improved by adding 30% pregelatinised flours from the native GPF or drum‐dried green banana flour (DDGBF) in combination with applying varied steps of cooking and/or cooling, which were applied after pasta extrusion prior to drying them. The study suggests that GPF, in its native form, but particularly when pregelatinised, is a promising ingredient to be used for the production of GF pasta.     

Effect of acid treatments and drying processes on physico-chemical and functional properties of cassava starch

The effects of acid treatments (HCl or organic acids) and drying processes (oven or sun) on the physico-chemical and functional properties of cassava starch have been studied. The objective was to obtain modified starches with expansion properties similar to those of sun dried fermented cassava starch (polvilho azedo) as produced by an empirical process. Expansion was evaluated using a baking test. Independent of the drying method, organic acid-hydrolysed cassava starch presented the same X-ray diffraction patterns (changes from C to A) and similar intrinsic viscosity values. SEM observations showed no differences between granule surfaces of sun dried and oven dried samples. However sun dried organic acid-hydrolysed starches presented lower paste consistency values at 30°C when compared with oven dried ones. HCl-modified cassava starches were oven or sun dried, giving biscuits with low specific volumes (2·5–3·1 ml g⁻¹). Similar behaviour was obtained using oven dried organic acid modified cassava starches. When submitted to sun drying, organic acid modified starches showed great improvements in biscuit expansion (5–10 ml g⁻¹). The highest average specific volumes were obtained using lactic acid modified starches. © 1998 SCI.     

Effects of vacuum and microwave freeze drying on microstructure and quality of potato slices

Potato slices immersed in 0.5% CaCl₂ solution for 10 min were examined using light microscopy for their microstructure in frozen state before drying, during the sublimation drying stage, in the desorption drying stage and in the final dried form. Additionally, the final dried product was also tested for vitamin C content, color, starch content, texture and sugar content. Experiments were carried out using conventional vacuum freeze dryer as well as a microwave freeze dryer. Results for both unblanched and blanched potato tissues, crystal growth during sublimation drying stage was observed to cause structural damage to the cell walls. Blanched tissue suffered more damage during the freezing process. Interestingly, microwave freeze drying yielded product similar in quality to that obtained in vacuum freeze drying with conductive heating.     

不同干燥方式对葛根全粉抗氧化性能和香气成分的影响

以葛根为原料,研究热风干燥、冷冻干燥、真空干燥对葛根全粉的基本成分、抗氧化性能和香气成分的影响。结果表明:不同干燥方式下葛根全粉的淀粉、粗蛋白、粗脂肪等基本成分含量差异显著(P0.05),冷冻干燥葛根全粉中总黄酮和总酚含量分别为2.46 g/100 g和1.37 g/100 g,显著高于其他2种干燥方式(P0.05);冷冻干燥所得葛根全粉的自由基清除力、还原力和金属离子螯合能力最高,而热风干燥所得产品的抗氧化能力最低。运用固相微萃取-气相色谱-质谱联用对鲜葛根和3种干燥方式葛根全粉的香气物质进行分析,鲜葛根、热风干燥、真空干燥和冷冻干燥全粉各自鉴定出43、68、66种和64种挥发性香气成分。真空干燥和冷冻干燥对于鲜葛根中的香气成分有更好的保留和增加效果,并且减少了部分对风味有反作用的物质。     

Functional group changes and chemical bond-dependent dielectric properties of lotus seed flour with microwave vacuum drying

Microwave vacuum drying (MVD) was applied to dehydrate lotus (Nelumbo nucifera Gaertn.) seeds. This paper evaluated the changes of molecular, crystalline, and morphological structural properties of lotus seeds after MVD. The results showed the frequency of δ(CH) bending, β(CH), ν(OH), and carbon–oxygen double bonds (C = O) increased with increasing microwave power density. Moreover, as microwave power density increased, the transition enthalpy of crystallinity gradually increased, which was related to the formation of crystalline starch, re-crystallization, and complexes of starch–lipid structure depending on the hydrogen bonds formed. The MVD process resulted molecular polarity of lotus seeds, whereas the dielectric properties also changed. The dielectric properties interacted with the changes of molecules and crystalline structure. The morphology of lotus seed flour changed because the shape of starch granules was disrupted and the granules became aggregated with nonstarch components as the microwave power density increased. All these results explain the interactions among polymer molecules in lotus seeds dried by MVD.     

Combined Smoking and Drying Kinetics of Retted Cassava Pulp and Effects on the Physicochemical and Pasting Properties of the Extracted Starch

Cooked paste of smoked-dried flour of retted cassava is the staple food of million people in West and Central Africa. The present study investigates the dynamics of combined smoking and drying on some physicochemical and functional properties of the flour and its derived starch. Fresh cassava tubers (variety 4115) were trimmed, retted, wrung, crushed, put into balls and then dried using three processes: traditional combined smoking and drying, electrical combined smoking and drying, and oven-drying. The drying processes did not significantly modify (p?>?0.05) the proximate composition of samples neither their drying rates (0.19 h^?1?<?k?<?0.22 h^?1). A positive and significant correlation was shown between the drying constant k and the smoking constant k _s (p?<?0.05). The colour of the oven-dried flour sample was clearer with the highest whiteness index (86.11?±?0.76) than the flour from traditional and electrical combined smoking and drying processes (65.41?±?4.35 and 68.18?±?3.98, respectively). The peak viscosity and breakdown values of retted starch paste were significantly higher (p?<?0.05) than that of the flour from which it originated. Meanwhile, the starch cold paste exhibited lower setback values and thus a lesser tendency to retrogradation when compared to retted flour gel. All this suggests that despite the relative instability of temperature in the traditional attic, it preserves, in comparable extent, the functional and nutritional values of cassava derivatives as electrical drying processes. Considering the functional use of the retted cassava for fufu preparation, smoked-dried starch is more suitable for cooking than oven-dried starch. In addition, the electrical combined smoking and drying process appeared as the best drying method, since the derived product has low tendency to retrogradation.     

Effect of drying temperatures on chemical and morphological properties of acorn flours

Drying curves at different temperatures were established for Quercus suber and Quercus rotundifolia fruits. Flours produced by milling fruits dried at different conditions were evaluated for colour, starch granules morphology, amylose and sugars content. The drying temperature was positively related to the reducing sugar content and negatively to starch content. The amilose content generally increased with drying temperature and the effect was more evident for the Q. rotundifolia . Results showed that flour colour parameters generally decreased with increased drying temperature. However, the drying temperature does not seem to affect starch morphology. It can also be stated that Q. suber produced darker flours, higher amylose and reducing sugar content, and bigger starch granules. Q. rotundifolia showed a lower level of damaged starch and higher fat and disaccharides content. According to the results, it was possible to conclude that drying temperature exerted marked effects on the properties of acorn flours in both studied species.     

Characterization of Phosphate Monoester Resistant Starch

The properties and structures of corn, wheat, and potato native starches and their phosphate monoester resistant starches were tested and compared. The results indicated that the resistant starch content, light transmittance, and freeze-thaw stability of the phosphate monoester resistant starch increased after modification. The native starches exhibited much higher peak viscosities compared with resistant starch (RS) and phosphate monoester resistant starches. The phosphate monoester resistant starch from corn and wheat starch exhibited a higher peak and final viscosity and lower gelatinization temperatures compared with the resistant starch, while the peak and final viscosity of the potato phosphate monoester resistant starch samples were lower than that of potato resistant starch. In the FT-IR graph, a new peak at 1244 cm^?1 (P=O bond) was observed for all kinds of phosphate monoester resistant starch.     

Physicochemical properties of octenyl succinic anhydride‐modified potato starch with different degrees of substitution

BACKGROUND: Esterified starch is an important type of modified starch. In particular, octenyl succinic anhydride‐modified starch (OSA starch) is widely used in the food industry. However, there has been little research on the properties of products with different degrees of substitution (DS). Therefore the aim of this study was to analyse the physicochemical properties of products with different DS. RESULTS: OSA starch samples with different DS were prepared from potato starch. Two new peaks were observed in the Fourier transform infrared spectrum, one at 1724 cm^?1 due to C?O and one at 1572 cm^?1 due to RCOO? . Emulsifying capacity and emulsion stability improved with increasing DS. Rheological analysis showed the occurrence of the ‘shear‐thinning’ phenomenon, the viscosity of the sample with DS = 0.0211 being even lower than that of native starch. A decrease in syneresis rate from 88.3% (native starch) to 39.0% (DS = 0.0211) indicated that freeze–thaw stability was improved. CONCLUSION: The physicochemical properties of OSA potato starch were better than those of native potato starch. Freeze–thaw stability, emulsifying capacity and emulsion stability improved with increasing DS. Viscosity increased at lower DS but decreased at DS = 0.0211. Copyright © 2009 Society of Chemical Industry     

Development and characterization of extruded snacks from New Zealand Taewa (Maori potato) flours

Crispy extruded snacks were prepared by mixing ungelatinized dried potato flours from four different Taewa cultivars and a modern potato cultivar with corn flour at two different ratios (25:75; 50:50), and their quality characteristics studied. All of the potato flours showed differences in colour, dry matter content, starch content and pasting characteristics. Among the extrudates prepared with 25% potato flours, Huakaroro snacks showed an L¹ value of 51.71, whereas pure corn flour snacks had the highest L¹ value of 61.22. The b¹ at both levels of potato flour incorporation were lowest for Tutaekuri snacks. The microstructural characteristics of the extrudates such as cell structure and cell wall thickness changed considerably when potato flour was incorporated (50%) in the extruder feed. Moemoe, Tutaekuri and 100% corn flour snacks had the highest toughness, whereas the highest crispness was observed for the Huakaroro snacks. Lower and higher cold peak viscosities of 91 and 597 cP were observed for corn and Tutaekuri extrudates (in powdered form), respectively. The extrudates with 50% potato flour had higher breakdown and lower final viscosity than those containing 25% flour. The peak G′ values were highest for 100% corn, Moemoe and Karuparera snack pastes.     

干燥方法对猪血清物化性质的影响

为了提高畜禽屠宰副产物畜禽血的综合利用,减少资源浪费,降低环境污染,本文以猪血为原料,探讨了不同干燥方式对畜禽血血清物化性质的影响。通过比较真空干燥、鼓风干燥和冷冻干燥对血清蛋白,血清粉的复水性、可溶性肽含量、水解度及色泽的影响,发现冷冻和鼓风干燥对血清蛋白影响较小,仅在分子量50 ku~75 ku之间出现部分聚合血清蛋白;真空干燥导致较多血清蛋白聚合,产生较多分子量大于100 ku的蛋白质;冷冻干燥血清粉的复水性优于真空和鼓风干燥,用去离子水浸泡2 h即可完全溶解,而鼓风和真空干燥血清的复水性较差,不能完全溶解;冷冻干燥血清粉的可溶性肽及水解度均显著(p0.05)高于鼓风干燥和真空干燥,鼓风干燥血清粉的可溶性肽及水解度均显著(p0.05)高于真空干燥;冷冻干燥血清粉的色差值显著(p0.05)高于鼓风和真空干燥样品。     

干燥工艺对甘薯淀粉回生率影响

以甘薯淀粉为原材料,以甘薯淀粉回生率为指标,研究常温、太阳晒、真空减压、干燥箱和微波干燥等不同干燥工艺对甘薯回生抗性淀粉生成率影响。结果表明,各干燥最佳工艺参数为:常温下大气温度为16℃～19℃、大气湿度为68%～80%时,老化后甘薯淀粉5 d达至恒重,回生率由3.5%提高到4.5%,提高28.5%;阳光照射下,大气温度为23℃～36℃、大气湿度为42%～74%时,老化后甘薯淀粉5 d达至恒重,回生率由3.5%提高到4.7%,提高34.2%;真空干燥箱温度为120℃、真空度为0.08 MPa时,甘薯淀粉回生率最大,为14.62%,比空白提高3.1倍;干燥箱温度为90℃时,甘薯淀粉回生率最大,为12.24%,比空白提高2.5倍;微波温度为45℃时,甘薯淀粉回生率最大,为7.12%,比空白提高1倍;相比之下,真空干燥有利于甘薯淀粉回生。